Frontiers in Energy Research: January 2013

All-Solid-State Solar Technology Opens Bigger Window to the Sun

New, cheap, green and efficient solar cells were invented to do better

A three-dimensional look at the perovskite structure of CsSnI3 at room temperature (distorted 3D view). The red polyhedron represents the tin and iodine (specifically [SnI6/2]−). The yellow spheres represent cesium.

Wenbo Yan

The limitations of conventional solar cells include high production costs, low operating efficiency and durability and many cells' reliance on toxic and corrosive liquids. Interdisciplinary collaboration between scientists at Argonne-Northwestern Solar Energy Research Center, or ANSER, has resulted in a new type of all-solid-state dye-sensitized solar cell, or DSC, that, in principle, will minimize all of these solar energy technology limitations and replace the leaking and expensive conventional DSCs.

Solar energy can be stored by exposing an organic dye molecule to sunlight, which is absorbed by the molecule and converted to electricity. This process mimics photosynthesis in plants.

Typical DSCs are much cheaper than the conventional semiconductor solar cells, which dominate today’s commercial market. But the DSCs suffer from durability problems that come from their use of organic liquid electrolytes, which result in a leaking and corrosive cell in only a few months.

To solve this problem and make DSCs commercially available without losing their ability to efficiently convert sunlight to electricity, the team replaced the organic liquid electrolyte with a new inorganic material that actually starts as a liquid but ends up as a solid mass. The result is a new all-solid-state solar cell that is inherently more stable.

The new solar cell consists of porous titanium oxide, dye and a three-component compound including cesium, tin and iodine, shorthanded CsSnI3. The excellent solubility of CsSnI3 in a lot of solvents makes it easily transferable to the titanium oxide pores. Dried under nitrogen, the compound constructs an intimate contact with the dye molecules and the titanium oxide. Besides that, the electrons in CsSnI3 move very fast at room temperature, making it favorable for solar cell applications. This new cell shows conversion efficiencies of up to 10.2%, which are the highest seen so far for all reported solid-state DSCs. These conversion efficiencies are close to the highest value of the conventional DSCs, approximately 11 to 12%.

By replacing the liquid organic electrolyte with CsSnI3 powder, the new type of all-solid-state DSCs is able to solve the durability problems of conventional solar cell and possibly go through the challenge of long-term stability and commercialization.

Acknowledgments:

This work was supported by the Argonne-Northwestern Solar Energy Research, an Energy Frontier Research Center, funded by the Department of Energy, Office of Science, Office of Basic Energy Sciences. The National Science Foundation supported RPH Chang, who designed and fabricated the solar cells.

About the author:

Wenbo Yan is a Ph.D. student at University of California-Irvine, a member of the Center for Nanostuctures for Electrical Energy Storage based in University of Maryland at College Park. She is interested in making mesoporous manganese oxide nanowires for supercapacitors and lithium batteries.

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